#8251: traceback when computing E.torsion_subgroup() for an elliptic curve E
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Reporter: was | Owner: cremona
Type: defect | Status: new
Priority: critical | Milestone: sage-4.5
Component: elliptic curves | Keywords:
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Changes (by cremona):
* cc: robertwb, was (added)
Comment:
This error has (a) nothing to do with elliptic curve code and (b) nothing
to do with number fields at all!
It is arising because in several places in Sage source code the field of
rational numbers is referred to as {{{RationalField()}}} instead of as QQ.
This should not matter, since the {{{RationalField()}}} call is supposed
to return the unique object of its class, which is pre-assigned to QQ, but
apparently sometimes it does go through the process of running the code in
{{{RationalField.__init__()}}}. That code contains the mysterious line
{{{
self._assign_names(('x',),normalize=False) # ???
}}}
-- note that some one (not me) has added those ??? -- I cannot see any
reason for assigning any "names" to QQ. It is this call to the
_assign_names() function which sometimes raises the error. I do not know
why it only happens sometimes.
It might therefore be a good idea to change the title of this ticket. I
will ask other people for their opinion. Robert? (You added the ???)
William? (You added the assign_names line!)
I would like to try commenting out that line and testing the entire Sage
library.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/8251#comment:2>
Sage <http://www.sagemath.org>
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